This invention relates to a reflection density measuring system in which light is projected onto a surface to be measured and reflected light from the measured surface is received by a photodetector, whereby the reflection density of the surface is measured.
2. Description of the Prior Art
There has been put into practice a dry-type chemical assay slide for quantitative analysis of a particular component contained in a droplet of a sample liquid such as blood or urine. See for example Japanese Patent Publication No. 53(1978)-21677, Japanese Unexamined Patent Publication No. 55(1980)-164356.
When analyzing chemical components in a sample liquid using such a chemical assay slide, a droplet of the sample liquid is deposited on the slide and is held at a constant temperature for a predetermined time in an incubator to permit a coloring reaction, and the optical density of the color formed by the coloring reaction is optically measured. That is, measuring light containing a wavelength selected in advance according to the combination of the component to be measured in he sample liquid and the reagent contained in the reagent layer of the slide is projected onto the chemical assay slide and the optical density of the reflected light is measured. Then the content of the component to be measured is quantified on the basis of the optical density of the reflected light by colorimetry.
The optical density of the reflected light is measured by a reflection density measuring system. In the reflection density measuring system, a sample or a chemical assay slide is mounted on the system, light is projected onto a surface of the slide to be measured and reflected light from the surface to be measured is received by a photodetector.
In such a reflection density measuring system, there has been a problem that the position of the measured surface of the sample can fluctuate in the direction perpendicular to the measured surface due to fluctuation in the positioning accuracy or the dimensional accuracy of the slide, deflection of the slide, and the like. When the position of the measured surface fluctuates in the direction perpendicular thereto, the relative position between the measured surface and the photodetector varies to change the result of the measurement.